This invention concerns a welding wire for use in submerged arc welding of Cr-Mo steels capable of obtaining a weld metal with excellent notch toughness and high tensile strength by adding boron and nitrogen as essential elements, as well as at least one of titanium, zirconium and aluminum to the wire.
Cr-Mo steels, for example, 21/2Cr - 1Mo steel and 9Cr - 2Mo steel are excellent materials of high temperature oxidation-stability and high temperature strength, and they are used in petrochemical facilities and boilers which are operated at high temperature and pressures.
However, since the circumstantial conditions for these materials have become severer in recent years, increasing demands have now been present for welding materials capable of obtaining excellent toughness at low temperature in view of the embrittlement of the materials during operation.
However, the welding materials conventionally employed so far, although having a practical performance with respect to the high temperature oxidation resistance by the control of chromium content, are still poor in tensile properties at elevated temperature including creep-rupture properties and in the notch toughness at low temperatures and can no more satisfy the recent strict demand, particularly, for the requirements of high strength and toughness.